Technical Field
Embodiments described herein are related to monitoring power supply voltages in an integrated circuit
Description of the Related Art
The supply voltage to an integrated circuit is nominally a constant-magnitude voltage. Real power supplies, however, can provide supply voltages that vary in magnitude base on instantaneous current demands of the circuit and the capabilities of the power supply that generates the supply voltage. For example, a large instantaneous current draw may cause the supply voltage to droop (reduced voltage magnitude). A rapid decrease in the current draw may cause overshoot (increased supply voltage magnitude). Viewing the variations in load and supply voltage magnitude in the frequency realm, significant frequency components at resonant frequencies of the integrated circuit, its packaging, and/or related circuitry can cause oscillation (“ringing”) on the supply voltage.
Supply voltage variation is modeled as part of the design process for an integrated circuit, but the complexity of the problem and the many sources of information needed to perform the analysis make the model inherently inaccurate. Complexities include variations in integrated circuit load, clock frequency which can change dynamically during operation, power supply characteristics, etc.
In some cases, fast analog to digital converters (ADCs) mounted on a circuit board with the packaged integrated circuit have been used to measure supply voltage characteristics in real time. Software may be executed to periodically read the ADC samples and form a representation of the variation in the supply voltage. However, when the integrated circuit can dynamically change modes (e.g. supply voltage magnitude and clock frequency settings), the measurements cannot be correlated to the mode in which the integrated circuit was operating. Additionally, the location of the ADC on the board prevents observation of the behavior of the power supply voltage at the integrated circuit semiconductor die, due to package parasitics that limit high frequency changes from being observed external to the package.